In a method referred to as link aggregation, or trunking, a device combines a set of one or more physical links into one logical link, called and aggregate link or trunk. The set of links is connected to another device that also has aggregated those links into an Aggregate Link.
A number of companies have announced plans that allow one or, both ends of the aggregate link to consist of a cluster of one or more cooperating devices. The devices may be for example switches. These cooperating devices are referred herein as cooperating link aggregation member devices, aggregation member devices, cooperating devices or cluster members. The cooperating devices use a separate communication path, the Intra-Cluster Interconnect, to coordinate communication with the connected end devices.
U.S. Pat. No. 6,195,351 discloses a Logical Switch Set (LSS) comprising two or more switches that act as a single packet forwarding device with specific connection rules. The single packet forwarding device is a single logical unit. The LSS may be used as either a redundant switch set (RSS) or as a Load Sharing Switch Set (LSSS). The maximum throughput of the LSSS increases with each additional switch. A LSSS can only interconnect with the other devices via trunked links that contain at least one physical connection to each switch. The RSS may include a trunk link connection and a resilient link connection. U.S. Pat. No. 6,195,351 is hereby incorporated by reference.
U.S. Pat. No. 6,195,349 discloses a packet based high speed mesh which forms a trunk cluster. The trunk cluster is constructed with a set of loosely coupled switches, a configuration protocol, trunked network interfaces, and optionally a reachablilty protocol. The trunk cluster provides a Logical LAN service. Each switch in the trunk cluster provides a single “shared LAN” by interconnecting two or more links. The edge devices attached to the links run a trunk configuration protocol. These attached edge devices view the trunked ports as if trunked ports are connected to a shared LAN with multiple other attached devices. U.S. Pat. No. 6,195,349 is hereby incorporated by reference.
U.S. Pat. No. 6,347,073 discloses a plurality of independent control lines used by I/O modules to determine which switch of a redundant switch set is the active or primary switch. Each line is driven by a different source. Each of these control lines are driven by one of a plurality of judges an each judge can read the other control lines which they are not driving. All the I/O modules can only read the control lines. Each judge makes a decision as to which switch should be the primary switch. Each decision is conveyed using the control lines. The I/O modules use these control lines to direct a multiplexer of the respective outside node to connect to the primary switch. A majority rules algorithm is used to always obtain the correct result in the face of a single error. U.S. Pat. No. 6,347,073 is hereby incorporated by reference.
U.S. Pat. No. 6,058,116 discloses an arrangement of trunk clusters and a method for interconnecting trunk clusters wherein the interconnection method has no single point of failure, the bandwidth between trunk clusters is not limited by the throughput of a single switch, and faults are contained within each trunk cluster. A trunked interconnection structure is provided between trunk clusters. Each switch of a trunk cluster has a logical port connected to a trunked port. The trunked port or trunk port provides a physical connection to each trunk switch of another trunk cluster. Each trunk switch of the another trunk cluster has a logical port connected to a trunked port which in turn has physical connections to each switch of the first trunk cluster. The trunked interconnect isolates faults to a single trunk cluster and there is no single point of failure and the total throughput is not limited to any single switches capacity. This always provides a single loop free path from one trunk cluster to the other or others. Multiple trunk clusters may be interconnected using point-to-point connections. A high throughput campus interconnect trunk cluster can be used to connect each building data center trunk cluster.
With a cluster of devices at the end of an aggregate link, an Intra-Cluster Interconnect (ICI) may be provided to coordinate the switches or cluster devices. However, if only one ICI is provided, some serious problems can occur when the ICI fails. These problems are, but are not limited to:                1. The devices in the cluster often can't determine if the ICI has failed or if devices in the cluster have failed. If the ICI has failed, but the devices are functioning, then the required failure recovery actions are often different, than if one of more of the devices has failed.        2. The overall functioning of the cluster can be degraded. The coordination functions are also used to optimize the throughput, of the cluster. Thus when the ICI is not available throughput is decreased.        